The surface or ground water used for irrigation in agricultural applications generally has low macro- and micronutrient content. The usual approach to enrichment of ground water for agricultural use is addition of chemical fertilizers. Chemical fertilizers create a high demand for increasingly expensive chemical raw materials and have an overall negative impact upon the environment. Chemical fertilizers applied to fields must first be broken down by soil microorganisms into bioavailable form before the crops can absorb them. Algae can break down chemical fertilizers in the soil and water and deliver those nutrients in immediately bioavailable form to the crop. Additionally, the microorganisms which are fed by the algae and the products that the algae produce break down the organic matter in the soil thereby releasing these nutrients to be absorbed by the crops.
Algae in the soil surface layers function autotrophically as green plants, utilizing their photosynthetic capabilities to convert carbon dioxide, nutrients, and inorganic nitrogen into cell substance by means of energy derived from sunlight. Soil algae are divided into Chlorophyta or green algae, Cyanophyta or blue-green algae, Bacillariophyta or diatoms, and Xanthophyta or yellow-green algae. Blue-green algae are prokaryotic, and many, but not all, species fix nitrogen. Green algae are eukaryotic and do not fix nitrogen. Some species of green or blue-green algae are unicellular and others are filamentous. Although algae usually reproduce asexually by cell fission, they types can also reproduce sexually.
Certain photosynthetic microorganisms, especially algae, have been found to help control erosion, improve moisture retention, enhance soil aggregation, provide nutrients and organic matter to the soil, and reduce non sodium and chloride salinity. Algae cultures can be applied to the soil easily, for example, by mixing with water delivering the suspension to the soil in irrigation or sprayer. Algae can also be grown at the same time as the cash crop, with minimal competition for nutrients, space, sunlight, or moisture.
Algae, such as microalgae, have been added to soil in order to improve soil aggregation (U.S. Pat. No. 4,774,186) and to serve as a cover crop, which improves the soil for a cash crop, such as red clover. U.S. Pat. No. 3,969,844 discloses a method of treating soil with flocculent-producing algae and supplemental nutrients as a means for soil aggregation.
In addition to being used to improve soil aggregation, algae have been used to fix nitrogen. In particular, certain blue-green algae have been used in flooded rice fields for this purpose. The rice field ecosystem is a favorable environment for the growth of blue-green algae and that nitrogen fixation by blue-green algae plays a vital role in the buildup and maintenance of soil fertility in such fields. Release of nutrients through microbial decomposition after the death of the algae appears to be the principle means by which nitrogen is made available to the rice. Roger, P. A. and Kulasooriya, S. A., Blue-Green Algae and Rice (Manila: The International Rice Research Institute, 1980), pgs. 49-50, hereinafter Roger and Kulasooriya. The entire focus of Roger and Kulasooriya is on the use of blue-green algae for nitrogen fixation in flooded rice fields. In fact, they report that the use of the algae seems to have little effect on the physical properties of the soil, although it may improve soil aggregation. (Ibid, p. 7)
U.S. Pat. No. 6,083,293 discloses a method of enhancing crop production by applying a solution containing algae extract component, humus extract, nitrogen urea, and a yeast/molasses combination component to the crop. The inclusion of algae in a hydroculture crop production system (U.S. Pat. No. 5,121,708) has been disclosed.
U.S. Pat. No. 7,048,010 discloses that the presence of algae in an irrigation system is undesirable. Even so, the treatment of nutrient-rich water, i.e. waster water, with algae for removing nitrogen-containing and phosphorous-containing compounds from the water has been reported using a packaged algae filter having a medium for supporting algae growth and an artificial light source (U.S. Pat. No. 5,670,046) or using a bed of algae immobilized on a surface over which waste water flows to remove pollutants therein (U.S. Pat. No. 5,573,669) or using algae-containing tanks to treat water and remove pollutants (U.S. Pat. No. 5,389,257). Algae immobilized onto sheets have been suggested for use as a nutrient source for agricultural applications (U.S. Pat. No. 4,950,601). Algae have also been used to treat wastewater to form substantially purified effluent streams (U.S. Pat. No. 6,465,240).
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